Reland "Enable -Wextra-semi in mac builds that have dcheck_always_on set."

This is a reland of 5e12be6776a7014290c72d027d3e6123594da745

dawn's build files are now fixed, so enable it for debug builds too.

Original change's description:
> Enable -Wextra-semi in mac release builds that have dcheck_always_on set.
>
> Bug: 926235
> Change-Id: I32c7a9f15f1f544caaceef28b0d34ebd643aa35d
> Reviewed-on: https://chromium-review.googlesource.com/c/1486880
> Reviewed-by: Mark Mentovai <mark@chromium.org>
> Commit-Queue: Mark Mentovai <mark@chromium.org>
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Auto-Submit: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#635214}

Bug: 926235,935704
Change-Id: I488db4451a0751d59bb8057194ddcab0b3ea8ebf
Reviewed-on: https://chromium-review.googlesource.com/c/1488012
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635513}
1 file changed